<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div {
            position: relative;
            float: left;
            width: 200px;
            height: 300px;
            border: 1px solid #ccc;
            /*压住相邻的边框*/
            margin-left: -1px;
            margin-top: -1px;
        }
        /*鼠标经过改变边框的颜色*/
        div:hover {
            border: 1px solid #ff4400;
            z-index:1;
        }
    </style>
</head>
<body>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
</body>
</html>